This application is based on Patent Application No. 2001-343235 filed Feb. 9, 2001 in Japan, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to a card-edge connector (edge-socket connector) wherein a plurality of contact terminals formed therein are respectively brought into contact with a plurality of contact pads formed at one end of an edge board by loading the edge board into the connector, developed for electrically connecting the card-edge connector with a printed circuit board or a cable via such contact, particularly improved to a card-edge connector capable of reducing the temperature rise of the contact terminals and improved to prevent the latter from being entangled with each other.
2. Description of the Related Art
The card-edge connector is used for electrically connect an edge board to a main board or others of various electronic equipments. The edge board includes a plurality of electro-conductive contact pads arranged on one side or both sides of an end portion of a printed circuit board on which electric circuits are formed. The card-edge connector of this type generally has a rectangular housing. Also the card-edge connector has in the interior of the housing a recess into which the edge board is inserted and a plurality of elastic contact terminals arranged on one side or both sides of a member in which the recess is formed and others.
As such a card-edge connector, a double-sided type card-edge connector has been known for loading therein a double-sided edge board arranged the contact pads on both sides of a printed circuit board. In such a double-sided card-edge connector, a plus voltage is supplied to the contact pads on one side of the edge board and a minus voltage is supplied to those on the other side thereof when an electrical power is supplied to the edge-connector from a main board including the connector, or when a large power is supplied to the edge board through cable or the like for connection with the edge-connector.
The contact terminal to be brought into contact with the contact pad is formed of a spring piece. The contact terminal includes a terminal section to be electrically connected to the main board or a cable, a fixed part secured to a connector housing, a spring piece section consecutive to the fixed part and a contact point section.
In the conventional card-edge connector, one contact terminal corresponds to each of the contact pads in the edge board is provided. Since it is designed that one contact point section of the respective contact terminal is brought into contact with the contact pad (a one-point contact), the temperature can rise in all of the terminal section, the fixed part, the spring piece section and the contact point section in the respective contact terminal when a large power is supplied to the edge board whereby a large current flows between the contact section of the respective contact terminal and the contact pad. Accordingly, the conventional card-edge connector has a problem in that the rated current becomes low.
The present invention has been made in consideration of such circumstances, and an object thereof is to provide a card-edge connector capable of enhancing the rated current even if a large power is supplied to the respective contact terminal of a card-edge connector, has additional advantage of being able to prevent the contact terminals from entangling with each other.
In an aspect of the present invention, there is provided a card-edge connector comprising a connector housing having a recess into which is inserted a printed circuit board having a plurality of contact pads arranged on at least one side of an end portion thereof, and
a plurality of contact terminals, each having a fixed part to be secured to the connector housing, an elastically deformable spring piece section extending from the fixed part and having a contact point section at a distal end thereof; the card-edge connector bringing the contact pads on the printed circuit board inserted thereinto into contact with the contact point sections of the plurality of contact terminals,
wherein the contact terminal is formed of a plurality of contact units stacked with each other so that the contact point sections of the respective contact units in each layer are distributed to disperse in the lengthwise direction of the contact terminal within the contact pad, and
spring piece sections of the contact units except an innermost contact unit is folded back at a midpoint to be formed a hook-shape, a contact point section of the innermost contact unit is formed to arcuate-shape, and
a distal end of the innermost contact unit in the plurality of stacked contact units extends to a position at which it is not entangled with a distal end of the adjacent contact unit.
The temperature rise of the contact terminal is determined by the conductor resistance of the contact terminal, and the smaller the resistance, the less the temperature rise. The conductor resistance of the contact terminal is determined by a dielectric constant inherent to material of the contact terminal and a cross-sectional area of a portion through which the electric current flows, wherein if the contact terminals are made of the same material, one having a larger cross-sectional area is smaller in conductor resistance.
On the other hand, a contact resistance generates in the contact terminal at a position brought into contact with the contact pad of the printed circuit board; i.e., a contact point section. The contact resistance is determined by an area of the contact point section of the contact terminal with the contact pad, and the larger the contact area, the less the temperature rise. A size of the contact area is defined by a width of the contact point section and the number of contact point sections, and the larger the width of the contact point section and the more the contact point sections, the less the temperature rise.
According to the present invention, the temperature rise is restricted by forming one contact terminal from a plurality of contact units stacked together to increase a cross-sectional area of the contact terminal. In addition, the contact point sections of the respective stacked contact units are arranged to disperse in the lengthwise direction of the contact terminal within the contact pad, whereby the number of contact point sections increases to restrict the temperature rise.
In this regard, if the contact point sections of the respective contact units are brought into contact with a narrow area of the contact pad in the printed circuit board by using the plurality of stacked contact units, it is necessary to arrange the contact point sections of the respective contact units close to each other. Since the respective contact point sections of these contact units variously moves during the insertion and withdrawal of the printed circuit board, there may be a case in which the contact point section of one contact piece rides on that of the adjacent contact piece to entangle with each other. In such a case, the contact point sections of part of the contact units may not be brought into contact with the contact pads of the printed circuit board, whereby an effect is not obtainable which is to be expected from the contact terminal of the above-mentioned multi-contact point system.
Thus, in the present invention, the above-mentioned entanglement is prevented by extending a distal end portion of the innermost contact unit among the plurality of stacked contact units extends to a position at which it is not entangled with a hook-shaped distal end of the adjacent contact unit.
As described above, according to the present invention, the cross-sectional area of the contact terminal increases by constituting the contact terminal from a plurality of stacked contact units so that the temperature rise is restricted. Further, the contact point sections of the respective stacked contact units are arranged to disperse in the lengthwise direction of the contact terminal within the contact pad so that the number of contact point sections increases to restrict the temperature rise.
Also according to the present invention, since a distal end portion of the innermost contact unit among a plurality of stacked contact units extends to a position at which the former is not entangled with a distal end of the adjacent contact unit, the entanglement of the distal end portions of the respective contact units is assuredly prevented. Thus, it is possible to assuredly avoid the inferior contact of the contact unit to result in the expected effect due to the contact terminal having multi-contact points.
Also according to the present invention, since the spring piece section of the respective contact unit is split into a plurality of spring piece units in the widthwise direction it is possible to assuredly bring the contact point sections of the respective spring piece units into the contact pad.